Positioning apparatus

ABSTRACT

In the present positioning apparatus, a positioning apparatus, comprising: a box body including a process chamber exposed to a decompression environment in the interior of the box body and an opening allowing said process chamber to communicate with an outside; a moving member for shielding said opening of said box body with a slight clearance between said box body and the moving member and movable with respect to said opening of said box body; and a differential pumping seal for sealing said slight clearance between said opening of said box body and said moving member, wherein a portion of said moving member to be moved into the interior of said process chamber, when said moving member moves, is formed as an adsorption preventive area.

This is a Continuation of application Ser. No. 10/202,607 filed Jul. 25,2002, now U.S. Pat. No. 7,059,607. The entire disclosure of the priorapplication, application Ser. No. 10/202,607 is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a positioning apparatus which can movea work, for example, in a chamber insulated from the externalenvironment.

In a semiconductor manufacturing apparatus, when working a work, thework is moved while it is placed on a stage within a process chambermaintained at a vacuum atmosphere or at a specific gas atmosphere. Here,in case where a positioning apparatus including a drive source isdisposed within the process chamber, because the interior of the processchamber can be kept sealed with respect to the exterior of the processchamber, the vacuum atmosphere or specific gas atmosphere can bemaintained relatively easily.

However, in case where the positioning apparatus including a drivesource is disposed within the process chamber, the process chamberitself increases in size. This takes a lot of time to make the interiorof the process chamber reach a given level of pressure, requires a largequantity of specific gas for filling the interior of the processchamber, or makes it difficult to maintain the positioning apparatus.

On the other hand, in case where the capacity of the process chamber isminimized, the above-mentioned problems can be truly solved but there isrequired a structure in which the table for placing the work thereon canbe driven from the outside of the process chamber. As a structure ofthis type, there is known a structure in which there is disposed amoving shaft extending between the interior and exterior of the processchamber through an opening formed in the wall of a box body incommunication with the process chamber, and the moving shaft is movedwith respect to the box body to thereby drive the table existing in theinterior of the process chamber from the exterior of the processchamber. And, there is also known another structure in which there isdisposed a flat plate for shielding the surface of the opening of thebox body, and the flat plate is moved with respect to the box body tothereby drive a table existing in the interior of the process chamberand placed on the flat plate from the exterior of the process chamber.In either of these structures, a clearance between the box body andmoving shaft or flat plate is sealed by a differential pumping seal tothereby be able to maintain the environment of the interior of theprocess chamber (for example, see U.S. Pat. No. 4,191,385).

By the way, referring to the base material of the above-mentioned movingshaft or flat plate serving as a moving member, for example, for avacuum atmosphere, in some cases, there is used metal material such asstainless steel or aluminum alloy (which has received surface treatmentsuch as washing in order to reduce the gas release speed) which isexcellent in vacuum characteristic. Also, for example, in case where theinterior of the process chamber is held at a negative pressure, themoving shaft or flat plate is caused to receive a great force due to adifference in pressure between the interior and exterior of the processchamber; and, in case where the moving shaft or flat plate is flexed ordeformed, there is a fear that the positioning accuracy of the work canbe lowered. To avoid this, there is proposed an attempt to use ceramicmaterial light in weight (low in specific gravity) and high in rigidityas the base material of the moving shaft or flat plate. Since theceramic material is non-magnetic material, especially when an ion chargeapparatus or an electronic beam apparatus requiring a vacuum environmentand a low magnetic field variation is used to work a work existing inthe interior of the process chamber, it can be said that the ceramicmaterial is suitable for the moving shaft or flat plate.

However, because the normal ceramic material is sintered micro-particles(powder), due to occlusion of gas molecules (adsorption of gas moleculeswithin a capillary tube), when compared with metal material, a largequantity of gas is released. Further, when compared with metal material,it is difficult to enhance the surface roughness of the ceramic material(in the case of the normal ceramic material, the limit is Ra=approx. 100nm) and the actual area (adsorption area) of the ceramic material islarger than that of the metal material in case where they are equal insurface area to each other; and, as a result of this, a large quantityof gas is released. Therefore, in case where the surface of the ceramicmaterial, which has adsorbed the molecules of the air, advances into theinterior of the process chamber together with the movement of the movingshaft or flat plate, the accumulated air molecules are eliminated fromthe ceramic surface, which raises a fear that the pressure in theinterior of the process chamber can be raised or the density of thespecific atmosphere gas can be varied. Also, in case where, instead ofthe ceramic material, metal such as stainless steel is used as the blankmaterial of the moving shaft and flat plate, it is true that the surfaceroughness of the metal is better (that is, the surface area is smaller)than the ceramic material, but, in the case of metal atoms as well,there occurs such phenomenon as in the ceramic material, that is,adsorption of the molecules of the air; and, therefore, there is apossibility that there can be raised a similar problem.

However, even in case where there is used the metal material that, asdescribed above, is excellent in vacuum characteristic, in the portionof the moving member that is exposed to the air, adsorption of gasmolecules to the surface of the exposed portion cannot be avoided.Normally, in a vacuum apparatus, there can be obtained a good vacuumcondition through the following exhaust process, comprising: a step (1)of releasing the air from the interior of the vacuum apparatus; a step(2) of releasing gas molecules adsorbed to the inner wall of the vacuumapparatus; a step (3) of diffusing hydrogen gas from the composingmembers of the vacuum apparatus; and, a step (4) of allowing the air topermeate into the interior of the vacuum apparatus from the atmosphericenvironment.

However, in the conventional apparatus to which the differential pumpingseal is applied, the surface of the exposable portion of the movingmember, from which the adsorbed gas molecules have been released in avacuum environment, is allowed to move from the process chamber throughthe seal portion thereof to the atmospheric environment. Therefore,since the surface of the exposable portion with the adsorbed gasmolecules reduced in the vacuum environment, is exposed to theatmospheric environment, the adsorbed gas molecules are returned totheir initial states. And, in case where the exposable portion returnsinto the process chamber, the adsorbed gas molecules of the exposableportion are gradually released in the interior of the process chamber;and, this operation cycle is repeated. The repetition of this operationcycle deteriorates the degree of vacuum in the interior of the processchamber.

While the foregoing description has been given on the assumption thatthe process chamber is held at a vacuum atmosphere, the phenomenonoccurring on this assumption can be similarly found also in an apparatusin which a differential pumping seal is used in a high-density specificatmospheric gas process chamber. That is, there is a fear that gasmolecules existing in the exterior of the process chamber can move intothe interior of the process chamber along with the movement of a movingshaft or a flat plate to thereby vary the density of the gas existing inthe interior of the process chamber.

Here, in the above-mentioned conventional positioning apparatus, thereare found the following problems. Firstly, when the moving member ismoved into and out of the process chamber kept in the vacuumenvironment, the gas particles adsorbed to the surface of the movingmember in the exterior of the process chamber are released into thevacuum environment of the interior of the process chamber to therebychange the degree of vacuum in the interior of the process chamber. As ameasure to avoid this problem, it can be expected to reduce the area ofthe surface of the moving member which is moved into and out of theprocess chamber. Here, generally, the surface of the moving member isworked with a certain degree of accuracy in view of the fact that it isguided by a guide member. However, to work the surface of the movingmember with a higher degree of accuracy in order to reduce the surfacearea increases the cost of the moving member greatly. Therefore, thismeasure is not desirable. On the other hand, as a measure to cope withthe change in the degree of vacuum, it can be expected to cover thesurface of the moving member movable into and out of the process chamberwith inert gas. In this case, however, it is necessary to dispose astorage tank for storing the inert gas therein, which unfavorablyincreases the cost of the positioning apparatus. Also, it is normallynecessary to dispose a facility for collecting the inert gas and afacility for detecting the leakage of the inert gas.

SUMMARY OF THE INVENTION

The present invention aims at eliminating the drawbacks found in theabove-mentioned conventional positioning apparatus. Accordingly, it isan object of the present invention to provide a positioning apparatuswhich can effectively prevent gas molecules existing in the exterior ofthe process chamber from moving into the interior of the processchamber.

In attaining the object, according to a first aspect of the presentinvention, there is provided a positioning apparatus, comprising: a boxbody including a process chamber exposed to a decompression environmentin the interior of the box body and an opening allowing said processchamber to communicate with an outside; a moving member for shieldingsaid opening of said box body with a slight clearance between said boxbody and the moving member and movable with respect to said opening ofsaid box body; and a differential pumping seal for sealing said slightclearance between said opening of said box body and said moving member,wherein a portion of said moving member to be moved into the interior ofsaid process chamber, when said moving member moves, is formed as anadsorption preventive area.

In case where the present portion of the moving member is exposed to theinterior of the process chamber with gas molecules adsorbed to oroccluded to the surface of the present portion, the thus adsorbed oroccluded gas molecules are eliminated in the interior of the processchamber, which results in the lowered degree of vacuum in the interiorof the process chamber.

In view of this, according to the present invention, at least theportion of the moving member to be moved into the interior of theprocess chamber is formed as an adsorption preventive area through somemeans, whereby the excellent degree of vacuum in the interior of theprocess chamber can be maintained.

In addition, in the case of an “absorption” is not especially explainedin the claims or the specification, the “absorption” means not onlyabsorption onto a surface of the moving member but also occlusion intothe moving member.

Also, according a second aspect of the present invention, There isprovided a positioning apparatus as set forth in the first aspect of thepresent invention, wherein a width of a portion of said box body opposedto said moving body in a moving direction of said moving member is setequal to or larger than a moving amount of said moving member.

In this case, since the portion of the moving member to be moved intothe interior of the process chamber is always opposed to the box body orto the process chamber and is thereby always held at the negativepressure, gas molecules are hard to be adsorbed to or occluded to thesurface of the present portion.

Here, a portion of the moving member, which is opposed to the box body(including a differential pumping seal) and is to be moved into theinterior of the process chamber, corresponds to the adsorptionpreventive area. Due to the suction by the differential pumping seal,the adsorption or occlusion of the gas molecules to the surface of thepresent portion is difficult to occur.

As described above, a positioning apparatus according to the presentinvention comprises: a box body including a process chamber formed inthe interior thereof and an opening for allowing the process chamber tocommunicate with the outside; a moving member for shielding at leastpart of the opening of the box body and movable with respect to theopening of the box body; and, a differential pumping seal for sealing aclearance between the box body and moving member, wherein, in order toprevent the portion of the moving member exposed to the outside of thebox body due to the movement of the moving member from being moved intothe interior of the process chamber, the width of the portion of the boxbody opposed to the moving body in the moving direction of the movingmember is set equal to or larger than the moving amount of the movingmember. Thanks to this, even in case where gas molecules are adsorbed tothe surface of the portion of the moving member exposed to the exteriorof the process chamber, the present surface is prevented from movinginto the interior of the process chamber, thereby being able to protectthe environment of the interior of the process chamber.

Also, according to a third aspect of the present invention, there isprovided a positioning apparatus as set forth in the second aspect ofthe present invention, wherein a seal surface of said differentialpumping seal on said box body side includes a plurality of grooveportions so formed as to surround said opening, and said plurality ofgroove portions are respectively formed so as to communicate with theirassociated exhaust passages, and also wherein the width of thenear-to-process-chamber end of one of said groove portions being mostdistant from said process chamber to said process chamber in the movingdirection of said moving member is set equal to or larger than themoving amount of said moving member.

In this case, even when higher sealing performance is required,elimination of the gas molecules into the process chamber can berestricted more effectively. The sealing performance of the positioningapparatus can be enhanced further. Due to this, even when further highersealing performance is required, there can be obtained high sealingperformance with more certainty.

Moreover, according to a fourth aspect of the present invention, thereis provided a positioning apparatus as set forth in any one of thesecond aspect or the third aspect of the present invention, wherein ahydrostatic bearing using inert gas as a medium is disposed incombination with said differential pumping seal so as to adjoin the sideof said differential pumping seal situated near to an outside.

A hydrostatic bearing using inert gas as a medium may be disposed incombination with the differential pumping seal in such a manner that itadjoins the side of the differential pumping seal situated near to theoutside. Thanks to this, as the hydrostatic bearing and differentialpumping seal can be combined together as a unit, even in case where themoving member has a relatively large stroke, high sealing performancecan be obtained.

In attaining the object, according to a fifth aspect of the presentinvention, there is provided a positioning apparatus as set forth in thefirst aspect of the present invention, further including: a cover memberfor covering at least the portion of said moving member movable betweenan interior side and an exterior side of said process chamber on saidprocess chamber exterior side; and an air supply device for supplying adry air having lower humidity than the atmosphere of said processchamber exterior side into said cover member.

A portion of the moving member, which is covered with the cover memberand is to be moved into the interior of the process chamber, correspondsto the adsorption preventive area.

From researches made by the inventors, it has been found that, of thegas molecules adsorbed to the moving member and movable from theexterior of the process chamber into the interior thereof, the moistureoccupies a high percentage. That is, in case where, as the environmentto which the portion of the moving member movable into and out of theprocess chamber is exposed, there is used an environment filled with thedry air (that is, the air with the moisture component removedtherefrom), the amount of gas to be released into the interior of theprocess chamber can be restricted as effectively as in an environmentfilled with inert gas. Since the dry air can be obtained by removing themoisture from the air, when compared with creation of the inert gasenvironment, formation of the dry air environment makes it possible toreduce the time and labor for management and cost thereof effectively.

By the way, when the environment of the process chamber exterior sidecontains the air having the humidity of 50%, preferably, the dry air maybe the air having such humidity that can control variations in thepressure of the interior of the process chamber caused by the movementof the moving member down to 30% or less. In this case, the amount ofgas to be released into the interior of the process chamber can berestricted more effectively.

Also, more preferably, the dry air may be the air having the humidity of10% or less (that is, the air having such humidity that allows adew-point temperature with respect to the atmospheric pressure in theenvironment of the exterior side of the process chamber to be −15° C. orless in the exit portion of the air supply device). In this case, theamount of gas to be released into the interior of the process chambercan be restricted further more effectively.

Further, in case where the cover member consists of a hydrostaticbearing for guiding the moving member, the number of parts can bereduced and also the positioning apparatus can be made compact instructure.

Here, the term “differential pumping seal” means a member having thefollowing function: that is, by exhausting a gas existing, for example,in a slight clearance between two mutually opposing surfaces, theenvironments on the two sides with the opposed surfaces between them(for example, an atmospheric environment and a high-vacuum environment)can be kept in a constant state in a non-contact manner. Therefore, theterm “slight clearance” between the box body and moving member accordingto the present invention means a clearance of a level that allows thedifferential pumping seal to perform its seal effect effectively.

According to a ninth aspect of the present invention, there is provideda positioning apparatus as set forth in the first, second and fifthaspect of the present invention wherein said adsorption preventive areais formed such that at least the surface thereof is formed ofhigh-density material or is coated with a CVD film or a PVD film.

In attaining the above object, there may be provided a positioningapparatus, comprising: a box body including not only a process chamberformed in the interior thereof so as to be exposed to a decompressedenvironment but also an opening for allowing the process chamber tocommunicate with the outside; a moving member formed of ceramic materialfor shielding at least part of the opening of the box body and movablewith respect to the opening of the box body; and, a differential pumpingseal for sealing the opening of the box body and moving member withrespect to each other, wherein close-density material is disposed on thesurface of at least the portion of the moving member movable between theinterior and exterior of the process chamber.

Also, there may be provided a positioning apparatus, comprising: a boxbody including not only a process chamber formed in the interior thereofso as to be exposed to a decompressed environment but also an openingfor allowing said process chamber to communicate with the outside; amoving member formed of ceramic material for shielding at least part ofthe opening of the box body and movable with respect to the opening ofthe box body; and, a differential pumping seal for sealing the openingof said box body and moving member with respect to each other, wherein acoating is disposed on the surface of at least the portion of the movingmember movable between the interior and exterior of the process chamber.

Further, there may be provided a positioning apparatus, comprising: abox body including not only a process chamber formed in the interiorthereof so as to be exposed to a decompressed environment but also anopening for allowing the process chamber to communicate with theoutside; a moving member formed of metal material for shielding at leastpart of the opening of the box body and movable with respect to theopening of the box body; and, a differential pumping seal for sealingthe opening of the box body and moving member with respect to eachother, wherein a coating formed of non-metal material is disposed on thesurface of at least the portion of said moving member movable betweenthe interior and exterior of the process chamber.

As described above, a positioning apparatus according to the presentinvention comprises a box body including not only a process chamberformed in the interior thereof so as to be exposed to a decompressedenvironment but also an opening for allowing the process chamber tocommunicate with the outside, a moving member formed of ceramic materialsuch that it can shield at least part of the opening of the box body andit is able to move with respect to the opening of the box body, and adifferential pumping seal for sealing the opening of the box body andmoving member with respect to each other, while close-density materialis disposed on the surface of the portion of the moving member movablebetween the interior and exterior of the process chamber. Thanks tothis, in case where, as the base material of the moving member, there isused ceramic material which is light in weight (low in specific gravity)and high in rigidity, the deformation of the moving member can bereduced to thereby be able to enhance the positioning accuracy. Also,since ceramic material is non-magnetic material, especially when an ioncharge apparatus or an electronic beam apparatus requiring a vacuumenvironment and low magnetic field variations is used in working a workin the interior of the process chamber, there can be provided a moresuitable positioning apparatus. In addition to this, because theclose-density material is disposed on the surface of at least theportion of the moving member movable between the interior and exteriorof the process chamber, the adsorption of the gas molecules can berestricted to thereby be able to protect the environment of the interiorof the process chamber.

As an example of the close-density material of ceramic material, thereis available high-density ceramic in which the number of pores isreduced. Some of high-density ceramic can provide a good surface havingsurface roughness Ra of 100 nm or less. Especially, data on the“pore-free” (which is a trade mark registered by Nippon Ceratec Co.Ltd.) manufacture by Nippon Ceratec Co. Ltd. show that the “pore-free”material is superior to 99.9% alumina in the moisture eliminationcharacteristic. The “pore-free” material can form a high-accuracysurface having surface roughness Ra of 10 nm or less. Of course, afterthe high-density ceramic material is worked, it must be washedsufficiently. Unless it is washed sufficiently, the polished dregsremain in the pores, which gives rise to the pollution of the interiorof the process chamber.

Also, a positioning apparatus of the present invention comprises a boxbody including not only a process chamber formed in the interior thereofso as to be exposed to a decompressed environment but also an openingfor allowing the process chamber to communicate with the outside, amoving member formed of ceramic material such that it can shield atleast part of the opening of the box body and it is able to move withrespect to the opening of the box body, and a differential pumping sealfor sealing the opening of the box body and moving member with respectto each other, while a close-density coating is disposed on the surfaceof at least the portion of the moving member that is allowed to movebetween the interior and exterior of the process chamber. In case where,as the mother material of the moving member, there is used ceramicmaterial which is light in weight (low in specific gravity) and is highin rigidity, the deformation amount of the moving member can berestricted to thereby be able to enhance the positioning accuracythereof. Also, since the ceramic material is non-magnetic material,especially when an ion charge apparatus or an electronic beam apparatusrequiring a vacuum environment and low magnetic field variations is usedin working a work in the interior of the process chamber, there can beprovided a further suitable positioning apparatus. In addition to this,because the coating is disposed on the surface of at least the portionof the moving member that is allowed to move between the interior andexterior of the process chamber, the adsorption and elimination of thegas molecules can be restricted to thereby be able to protect theenvironment of the interior of the process chamber.

In the current technical level, in the case of the close-densitymaterial, especially, in the case of the large-sized close-densitymaterial, it is relatively difficult to provide a high-accuracy surfacehaving surface roughness Ra of 100 nm or less. On the other hand, byapplying the coating onto the necessary portion of ceramic, in the caseof the large-sized close-density material, the small pores thereof, towhich gas molecules can be easily adsorbed, can be closed at arelatively low cost, which makes it possible to reduce the substantialsurface area of the close-density material.

As the coating, a CVD film or a PVD film may be formed on the surface ofthe ceramic material. Specifically, for example, Sic (porous material)is used as the base material and the surface of the base material iscoated with the CVD film. As the other mother material, there can beused various kinds of ceramic material such as alumina, silicone nitrideand zirconia. On the other hand, as the coating material, there can alsobe effectively used other films such as PVD films which are formed ofTiN and TiC, and a sapphire film. Also, as the coating material, inorder to reduce the adsorption force with respect to the gas molecules,there may be preferably used non-metal material. Since the CVD film andPVD film are close-density material, they can have desired effects onthe porous ceramic material; that is, they can reduce the actual surfacearea of the porous ceramic material and thus can restrict the gasmolecule occlusion phenomenon. Also, a DLC film (hard carbon film) canalso be used. The DLC film can be obtained in both of CVD and PVD. And,even in case where metal material is used as the base material of themoving member, at least the surface of the portion of the moving member,which is allowed to move between the interior and exterior of theprocess chamber, may also be coated with non-metal material. Since asmetal base material, for example, there can be used stainless steel oraluminum alloy, there can be provided a moving member which is low incost; and, by applying the coating formed of the above-mentioned variouskinds of non-metal material onto the surface of the necessary portion ofthe metal base material, the gas molecules can be prevented from movinginto the interior of the process chamber from the surface of the movingmember.

Further, in order not only to minimize the adsorption of the gasmolecules under the atmospheric pressure but also to promote theelimination of the gas molecules, preferably, inert gas may be used asthe atmosphere gas for the atmospheric pressure. Since moisture is mostdisliked in the atmospheric environment as well, preferably, there maybe formed a dry (dehumidified) air atmosphere. Also, in case where aninert gas area of N₂ or argon is formed only in the portion which isclose to the seal area (for example, it is effective to spray the inertgas like an air curtain), the inert gas can be adsorbed firstly to thesurface of the movable portion which is allowed to move from the vacuumarea to the atmospheric pressure area, thereby being able to promote theelimination of the adsorbed gas molecules.

Here, the term “differential pumping seal” means a seal which exhaustsgas existing in a slight clearance between two mutually opposed surfacesto thereby keep two environments (for example, the atmospheric pressureenvironment and high vacuum environment) enclosing the two opposedsurfaces in a constant state and in a non-contact manner. In theembodiments to be discussed below, a member having an exhaust surface isreferred to as a differential pumping seal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front section view of a positioning apparatus 10 accordingto a first embodiment of the present invention;

FIG. 2 is an enlarged section view of the periphery of a differentialpumping seal 50, showing the absorption or occlusion and elimination ofgas molecules in a typified manner;

FIG. 3 is an enlarged section view of the periphery of a differentialpumping seal employed in a positioning apparatus according to a secondembodiment of the present invention;

FIG. 4 is an enlarged section view of the periphery of a differentialpumping seal employed in a positioning apparatus according to a thirdembodiment of the present invention; and,

FIG. 5 is an enlarged section view of the periphery of a differentialpumping seal employed in a positioning apparatus according to a fourthembodiment of the present invention;

FIG. 6 is a front section view of a positioning apparatus according to afifth embodiment of the present invention;

FIG. 7 is a partially omitted enlarged section view of the periphery ofa differential pumping seal having a structure shown in FIG. 6;

FIG. 8 is a front section view of a positioning apparatus according to asixth embodiment of the present invention;

FIG. 9 is a plan view of a positioning apparatus according to the sixthembodiment of the present invention;

FIG. 10 is a partially omitted enlarged section view of the periphery ofa differential pumping seal having a structure shown in FIG. 8;

FIG. 11 is a partially omitted enlarged section view of the periphery ofa differential pumping seal used in the seventh embodiment of thepresent invention;

FIG. 12 is a front section view of a positioning apparatus which is atest apparatus used in a test conducted by the inventors;

FIG. 13 is a graphical representation of the results of a test conductedon a comparison example 1;

FIG. 14 is a graphical representation of the results of a test conductedon an embodiment according to the present invention; and,

FIG. 15 is a graphical representation of the results of a test conductedon a comparison example 2; and

FIG. 16 is a front section view of a positioning apparatus 10 accordingto an eighth and a ninth embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, description will be given below of the preferred embodiments of apositioning apparatus according to the present invention with referenceto the accompanying drawings. FIG. 1 is a front section view of apositioning apparatus according to a first embodiment of the presentinvention, in which a differential pumping seal is shown in a simplifiedmanner. As shown in FIG. 1, a positioning apparatus 10 according to thepresent embodiment comprises a first box body 20 including not only aprocess chamber P and an opening 20 a which allows the process chamber Pto communicate with the outside, a moving block 30 disposed so as toshield the opening 20 a of the first box body 20, and a second box body40 disposed so as to be opposed to the first box body 20 with the movingblock 30 between them. The process chamber P is sucked by a pump P1through a pipe (which is shown in a simplified manner) and is therebyheld in a negative pressure environment. A decompression chamber R,which is formed in the interior of the second box body 40, is sucked bya pump P3 through a pipe (which is shown in a simplified manner) andthus it is similarly held in a negative pressure environment. By theway, the openings 20 a and 40 a are the same in shape and are disposedso as to be opposed to each other.

The moving block 30, with the two ends thereof supported by bearings(not shown), can be moved in the right and left direction in FIG. 1 by adrive part (not shown) (for example, a combination of a motor and a ballscrew, or a linear motor) and carries on the central portion thereof atable 31 for supporting a work (not shown). On the surfaces of theperiphery of the opening 20 a of the first box body 20 that are opposedto the moving block 30, there are disposed first differential pumpingseals 50 with a given clearance between them. On the other hand, on thesurfaces of the second box body 40 that are opposed to the moving block30, there are disposed second differential pumping seals 60 with a givenclearance between them. The first differential pumping seal 50 andsecond differential pumping seal 60 are respectively sucked by pumps P2through their associated pipes (which are shown in a simplified manner)to thereby seal the process chamber P and decompression chamber R withrespect to the outside. By the way, according to the present embodiment,the bearing surface (not shown) opposed to the upper surface of themoving block 30 constitutes a first guide surface, while the bearingsurface (not shown) opposed to the lower surface of the moving block 30constitutes a second guide surface.

Now, FIG. 2 is an enlarged section view of the periphery of the firstdifferential pumping seal 50, showing the adsorption and elimination ofgas molecules in a typified manner. The first differential pumping seal50 is formed so as to enclose the opening 20 a. Specifically, the lowersurfaces of the side walls 21 of the first box body 20, which aredisposed opposed to the surface of the moving block 30, provide sealsurfaces 50 a respectively including groove portions 51, 52 formed so asto extend along the opening 20 a; and, the first differential pumpingseal 50 further includes exhaust passages 53, 54 respectivelycommunicating from the groove portions 51, 52 to the pumps P2 which aredisposed externally of the first exhaust seal 50. Here, there is a fearthat the following problems can arise.

That is, in case where the moving block 30 moves to the left in FIG. 2,when gas molecules Am adsorbed to the upper surface of the moving block30 are opposed to the groove portion 52 due to the left-ward movement ofthe moving block 30, a major part of them are sucked by the pumps P2 andfurther, when the remaining adsorbed gas molecules Am are opposed to thegroove portion 51, most of them are sucked. However, the adsorbedgaseous molecules Am, which have not been sucked and thus remain stillon the moving block 30 upper surface, are eliminated in the interior ofthe process chamber P, which raises a fear that the negative pressure(or specific gas) environment of the process chamber P can be damaged.In the case of porous ceramic material, the occluded gas molecules Amare also eliminated in the interior of the process chamber P.

On the other hand, according to the present embodiment, as shown in FIG.1, since the width b of the side wall 21 of the first box body 20 (thatis, in FIG. 1, the right-and-left-direction length of the seal surface50 a of the first differential pumping seal 50) and the width b of theside wall 41 of the second box body 40 (that is, in FIG. 1, theright-and-left-direction length of the seal surface 60 a of the seconddifferential pumping seal 60) are set equal to or larger than therequired maximum stroke S of the moving block 30 (S≦b), the portion ofthe moving block 30 that is exposed to the exterior (the atmosphericpressure environment) of the process chamber P and decompression chamberR stays within the side wall 21 or side wall 41 even when the movingblock 30 moves up to the maximum stroke S, thereby being able torestrict the gas molecules Am from being eliminated into the processchamber P and decompression chamber R. By the way, the moving block 30serving as a moving member according to the present embodiment is madeof metal material. However, in case where, instead of the metalmaterial, the moving block 30 is made of ceramic material, there can beprovided another advantage that the present moving block can be madelight in weight and high in rigidity.

By the way, when the width b is larger than the thickness that isrequired of the side wall 21 of the first box body 20, only theright-and-left-direction (in FIG. 1) width (the width of the sealsurfaces 50 a, 60 a) of the differential pumping seals 50, 60 may be setfor b. That is, in the lower portion of the side wall 21 (upper portionof the side wall 41), there may be formed an edge portion which, in theright and left direction of FIG. 1, projects in the direction of theinterior of the process chamber P, or in the direction of theatmospheric pressure side, or in both directions.

Further, description will be given below of a device for restricting thedeformation of the moving block 30. Firstly, let us assume a case inwhich the second box body 40 is omitted. In this case, since theatmospheric pressure (about 10⁵ Pa) is always acting on the lowersurface of the moving block 30, the central portion of the upper surfaceof the moving block 30 is deformed in such a manner that it is pulledupwardly in FIG. 1. Even in case where such deformation is slight, theheight position of the table 31 varies, which makes it difficult to worka work with high accuracy.

On the other hand, in the present embodiment, since the second box body40 is disposed opposed to the first box body 20 and the decompressionchamber R formed in the interior of the second box body 40 is held in anegative pressure environment, the lower surface of the moving block 30is pulled downwardly in FIG. 1 to thereby restrict the deformation ofthe moving block 30 due to the negative pressure of the process chamberP, which makes it possible to keep the moving block 30 substantially ina no-deformation state. This can prevent the height position of thetable 31 from varying, so that the work positioning with high accuracycan be attained. Also, because the openings 20 a and 40 a are formed tohave the same shape and are disposed opposed to each other, thedeformation mode of the moving block 30 can be made to balance well andthus further-higher-accuracy positioning can be accomplished.

By the way, the degree of vacuum of the decompression chamber R need notbe coincident with the degree of vacuum of the interior of the processchamber P; for example, when the pressure of the interior of the processchamber P is set at 10⁻⁵ Pa, even in case where the pressure of thedecompression chamber R is set about 10⁻⁴ Pa (about 1/10 of theatmospheric pressure), the degree of deformation of the moving block 30can be reduced down to about 1/10 of the degree of deformation thatoccurs in the structure excluding the decompression chamber R. Thanks tothis, as the pump P3 of the decompression chamber R, there can be used apump which is lower in capacity and lower in cost, which makes itpossible to reduce the cost of the positioning apparatus. However, incase where there is formed in the moving block 30 a passage which allowsthe decompression chamber R and process chamber P to communicate witheach other, there can be omitted the pump P3 for the decompressionchamber R.

Now, FIG. 3 is a section view of the periphery of a differential pumpingseal used in a positioning apparatus according to a second embodiment ofthe present invention. In the embodiment shown in FIG. 3, a movingmember consists of a round shaft 130, while the round shaft 130penetrates through an opening 120 a formed in the side wall 121 of asingle box body 120. Only the portion of the side wall 121 surroundingthe opening 120 a is formed as a projecting portion 122; and, in theprojecting portion 122, there are formed two peripheral grooves 151, 152in such a manner that they are open to the opening 120 a. And, there arefurther formed two exhaust passages 153, 154 in such a manner that theyrespectively extend outwardly from the peripheral grooves 151, 152. Theexhaust passages 153, 154 are respectively connected to their associatedpumps P2 (FIG. 1). By the way, a differential pumping seal 150 arecomposed of the two peripheral grooves 151, 152 and two exhaust passages153, 154, while the opening 120 a serves as the seal surface of thedifferential pumping seal 150 on the box body 120 side. The thickness ofthe wall of the side wall 121 except for the projecting portion 122 iscontrolled down to the thickness that is necessary for a box body 120.The round shaft 130 is supported by a bearing (not shown) on theatmospheric side and can be moved in the right and left direction inFIG. 3 by a proper drive part which is also disposed under theatmospheric pressure environment but is not shown in FIG. 3. Also, sincethe shaft 130 is a round shaft, as the need arises, the round shaft 130can be driven so as to rotate about its axis.

In the present embodiment as well, as shown in FIG. 3, since the width bof the portion of the side wall 121 of the box body 120 that correspondsto the projecting portion 122 is set equal to or larger than the maximumstroke S of the round shaft 130 (S≦b), the portion of the round shaft130 that is exposed to the outside of the box body 120 (to theatmospheric pressure environment) still stays within the projectingportion 122 even in case where the round shaft 130 is moved up to themaximum quantity S, thereby being able to restrict the gas molecules Amfrom being eliminated into the interior of a process chamber P formed inthe interior of the box body 120.

Now, FIG. 4 is a section view of the periphery of a differential pumpingseal used in a positioning apparatus according to a third embodiment ofthe present invention. The embodiment shown in FIG. 4 is similar instructure to the embodiment shown in FIG. 3 except that the width b′ ofa projecting portion 122′ is set further larger than the maximum strokeamount S of the round shaft 130. Specifically, when the distance fromthe inner wall 120 b of the process chamber P to the inner wall 151 a ofthe peripheral groove 151 is expressed as c, the distance c is set insuch a manner that the relationship S≦c can hold. Therefore, the widthb′ is set large correspondingly to this. The reason for this is asfollows:

As can be judged from FIG. 2, at a position opposed to the peripheralgroove (here, 151) that is nearer to the outside of the box body 120,when compared with a position opposed to the peripheral groove (here,152) that is situated inwardly of the peripheral groove (151), thedegree of vacuum on the surface of the round shaft 130 is relativelylow. Therefore, it can be considered that gas molecules can be adsorbedin a small but some quantity to the surface of the round shaft 130 thatis exposed to the peripheral groove 151. Thus, especially when highsealing performance is required, for example, when the interior of theprocess chamber P must be held in a high degree of vacuum, or when themoving speed of the round shaft 130 is high, in case where the abovesurface moves into the process chamber P, there is a fear the gasmolecules adsorbed to the surface can be eliminated in the interior ofthe process chamber P. However, as in the present embodiment, in casewhere c and b′ are set such that S≦c holds, at least the surface of theround shaft 130 that is exposed to the peripheral groove 151 isprevented from moving into the interior of the process chamber P and,therefore, even when high sealing performance is required, eliminationof the gas molecules into the interior of the process chamber P can berestricted more effectively.

Further, in the case of S≦d shown in FIG. 4, of course, invasion of thegaseous molecules into the interior of the process chamber P can berestricted more effectively. However, in case where d increases, thewidth of the seal surface 120 a increases correspondingly to this, whichincreases a possibility that the round shaft 130 and box body 120 can becontacted with each other. That is, when taking it into considerationthat S≦c can sufficiently prevent the invasion of the gas molecules intothe interior of the process chamber P, more preferably, S≦c may beemployed.

Now, FIG. 5 is a section view of the periphery of a differential pumpingseal of a positioning apparatus according to a fourth embodiment of thepresent invention. Referring to the characteristic aspect of thestructure of the embodiment shown in FIG. 5, the end portion of the boxbody 120 shown in FIG. 3 is extended so that a bearing can be disposed.Specifically, a round shaft 230 penetrates through a circular-shapedopening 220 a formed in the long and narrow cylindrical-shapedprojecting portion 221 of a box body 220. A differential pumping seal250 comprises two peripheral grooves 251, 252 respectively open to theopening 220 a and two exhaust passages 253, 254 respectively extendingoutwardly from their associated peripheral grooves 251, 252. On the leftside (in FIG. 5) of the differential pumping seal 250, there is disposeda bearing 270 in the projecting portion 221 in such a manner that it issubstantially flush (it may be perfectly flush) with the opening 220 a.The bearing 270, which is a hydrostatic bearing, is connected to a pumpP3 through a passage 271 formed so as to penetrate through theprojecting portion 221 in the radial direction thereof and is used tosupport the round shaft 230 due to the positive pressure thereof in sucha manner that the round shaft 230 can be moved. By the way, adjacentlyto the bearing 270, in the portion of the projecting portion 221 that issituated on the differential pumping seal 250, there is formed a space255 (peripheral groove) open to the atmosphere through a passage (notshown). In the present embodiment, the portion of the opening 220 ahaving a depth b shown in FIG. 5 provides the box body side seal surfaceof the differential pumping seal 250.

In the present embodiment, as shown in FIG. 5, since the distance (thatis, the width of the seal surface) b between the process chamber P andspace 255 is set equal to or larger than the maximum stroke S of theround shaft 230 (S≦b), the portion of the round shaft 230 that isexposed to the space 255 (under the atmospheric pressure) still stayswithin the end portion 221 even in case where the round shaft 230 ismoved up to the maximum stroke S, thereby being able to restrict the gasmolecules Am from being eliminated into the interior of a processchamber P formed in the interior of the box body 220. Also, from theviewpoint of restriction of invasion of the gas molecules Am into theinterior of the process chamber P, more preferably, similarly to thepreviously-described embodiments, c shown in FIG. 5 may be set such thatS≦c or S≦d can hold.

Further, in order not only to minimize the adsorption of the gasmolecules under the atmospheric pressure but also to promote theelimination of the gas molecules, as the gas that is supplied to thehydrostatic bearing 270 by the pump P3, preferably, there may beemployed inert gas (for example, nitrogen gas and argon gas) which ishard to be adsorbed to the mating member of the hydrostatic bearing 270.With use of inert gas, in case where a and b shown in FIG. 5 are setsuch that S≦a+b, the above effects can be obtained. And, becausemoisture is most disliked in the atmospheric environment, desirably,there may be set a dry (dehumidified) air atmosphere. Also, in casewhere an inert gas (such as N₂ gas) area is disposed only in the areajust near to the seal area, the inert gas can be firstly adsorbed to thesurface of the moving portion which moves from the vacuum area to theatmospheric environment, thereby being able to promote the eliminationof the adsorbed gas molecules. As a specific structure for this, therecan be proposed a structure in which the inert gas such as N₂ gas ispressure fed from the pump P3 to thereby fill the periphery of thebearing 270 with the inert gas.

In addition, with use of the inert gas, in case where b and c shown inFIG. 5 are set such that S≦b or S≦c, the positioning apparatus of thepresent invention can be applied to the process chamber with strictcondition, for example, which requires higher vacuum.

Although the present invention has been described heretofore using thepreferred embodiments thereof, the present invention is not limited tothese embodiments but, of course, various changes and improvements arealso possible. For example, the moving block 30 may be moved in FIG. 1not only in the right and left direction but also in a directionperpendicular to the figure sheet, that is, may be moved in atwo-dimensional manner. In this case, the width b of the seal surface(not shown) of the side wall 21 extending in a direction perpendicularto the figure sheet is also set such that S≦b (in case where the strokein a direction perpendicular to the figure sheet is S). However, itmakes little sense to apply the present invention to a structure inwhich the round shafts 130, 230 are not moved in the axial directionthereof but are only rotated. Also, even in the case of suchflat-surface-shaped moving block as shown in FIG. 1, the width thereof,which corresponds to c or d in FIG. 4 showing the third embodiment ofthe present invention, may also be set equal to or larger than S.Further, in the case of such flat-surface-shaped moving block as shownin FIG. 1, a hydrostatic bearing may also be disposed in combinationwith the moving block in such a manner that it is adjoins the movingblock and is situated nearer to the atmospheric pressure side than thedifferential pumping seal. As the gas to be supplied to the hydrostaticbearing, there may be used inert gas. In this case, the width of thesurface of the box body that is opposed to the moving block can bedecided in accordance with the fourth embodiment of the presentinvention.

Now, description will be given below of the preferred embodiments of apositioning apparatus according to the present invention with referenceto the accompanying drawings. FIG. 6 is a front section view of apositioning apparatus according to a fifth embodiment of the presentinvention, with a differential pumping seal shown in a typified manner.FIG. 7 is a partially omitted enlarged section view of the periphery ofthe differential pumping seal having the structure shown in FIG. 6.

As shown in FIG. 6 or 7, a positioning apparatus 10 according to thepresent embodiment comprises a box body 320 including not only a processchamber P formed in the interior thereof but also two circular-shapedopenings 320 a, 320 a respectively formed in the two side walls thereoffor allowing the interior of the process chamber P to communicate withthe outside of the process chamber P, a moving shaft 330 serving as amoving member disposed so as to penetrate through the two openings 320a, 320 a, a drive part 340 for driving the moving shaft 330, twodifferential pumping seals 350, and two cover members 360. The interiorof the process chamber P is sucked by an exhaust pump P1 through a pipewhich is shown in a simplified manner in FIG. 6 to thereby provide anegative pressure environment.

The moving shaft 330, the two end portions of which are respectivelysupported by bearings (not shown), can be moved in the right and leftdirection in FIG. 6 by the drive part (for example, a combination of amotor and a ball screw, or a linear motor) 340 disposed under theatmospheric pressure, and also carries on the central portion thereof atable 31 for supporting a work (not shown). The inner peripheralsurfaces of the openings 320 a, 320 a of the box body 320 constitute theexhaust surfaces of the differential pumping seals 350, 350. Thedifferential pumping seals 350, 350 are respectively sucked by theirassociated exhaust pumps P2, P2 through pipes (which are shown in asimplified manner in FIG. 6) to thereby seal the interior and exteriorof the process chamber P against each other.

In FIG. 7, in the inner peripheral surface of the opening 320 a on theright side, there are formed a pair of peripheral grooves (which arealso referred to as differential pressure chambers) 320 b, 320 b. Theinteriors of these peripheral grooves 320, 320 b are respectively suckedby exhaust pumps P2, P2 through exhaust holes 320 c, 320 c penetratingthrough the side wall of the box body 320 to thereby provide negativepressure environments. The thus-formed negative pressure environments ofthe peripheral grooves 320, 320 b suck gas existing in a slightclearance between the opening 320 a and moving shaft 330 to therebyperform the sealing function.

As shown in FIG. 7, on the exterior side of the box body 320, adjacentlyto the opening 320 a, there is disposed the cover member 360 which iscomposed of a cylindrical portion 361 and a flange portion 362 having anopening 362. The moving shaft 330 penetrates through the opening 362 ofthe flange portion 362. The dry air can be supplied through a pipe 363from an air drier AD to a space existing in the interior of the covermember 360. The air drier (which is also referred to as an air supplyapparatus) AD is used to remove foreign substances such as moisture fromthe air and supply the clean air. For example, there is available an airdrier which cools the compressed air, separate the condensed moisturetherefrom, and then return it to its original pressure. Also, there canbe used other various types of air driers such as an air drier of a socalled heatless type and a membrane air drier. Or, there may also beused an air drier structured such that it sucks in the air and passesthe air through a chamber with a desiccant contained therein to therebyobtain the dry air. The dimension of the cover member 360 is set suchthat, even in case where the moving shaft 330 moves up to the maximumamount, at least the portion of the moving shaft 330 movable into theinterior of the process chamber P can be prevented from movingexternally of the cover member 360. By the way, the differential pumpingseal 350 and cover member 360, which are disposed on the left side, aresimilar in structure to the above-mentioned differential pumping seal350 and cover member 360 on the right side.

In case where the moving shaft 330 moved in the axial direction thereof,when the gas molecules adsorbed to the surface of the moving shaft 330become opposed to the peripheral groove 320 b situated on the exteriorside due to the movement of the moving shaft 330, most of them aresucked by the pumps P2; and also, when the gas molecules become opposedto the peripheral groove 320 b situated on the interior side, most ofthe remaining gas molecules are sucked; whereas the still unsucked andremaining gas molecules are eliminated in the interior of the processchamber P, thereby raising a fear that the-thus-eliminated gas moleculescan degrade the negative pressure (or specific gas) environment. In viewof this, in the present embodiment, the exterior side of the opening 320a is covered with the cover member 360 and the interior of the covermember 360 is filled with the dry air (that is, the air with themoisture removed therefrom) supplied by the air drier AD to therebyrestrict the adsorption of the gas molecules (especially, the moleculesof water) to the surface of the moving shaft 330. Thus, according to thepresent embodiment, the above-mentioned problem found in theconventional positioning apparatus can be solved.

By the way, as shown in the test results that will be discussed later,preferably, in case where the dry air filling the interior of the covermember 360 is the air having such humidity capable of restricting achange in the pressure of the interior of the process chamber P due tothe movement of the moving shaft 330 down to 30% or less (that is, suchhumidity of less than 50%) when the environment (the air) of the outsideof the box body 320 is filled with the air having humidity of 50%, theamount of gas to be released into the interior of the process chamber Pcan be restricted further. Also, more preferably, in case where the dryair is the air having humidity of 10% or less at room temperature andunder the atmospheric pressure (the air having such humidity that, inthe vicinity of the exit of the air from the air drier AD, provides thedew-point temperature of −15° or lower with respect to the atmosphericpressure in the environment of the outside of the box body 320), theamount of gas to be released into the interior of the process chamber Pcan be restricted still further.

Especially, according to the present embodiment, as the base material ofthe moving shaft 330, there can be used stainless steel such as SUS304which is easy to obtain. Also, even in case where a special surfacetreatment is not enforced on the surface of the moving shaft 330, oreven in case where such precise work as to control the surface roughnessdown to a low level is not enforced on the surface of the moving shaft330, the amount of the gas molecules to be adsorbed to the surface ofthe moving shaft 330 can be restricted similarly to a case in which theinterior of the cover member 360 is filled with the inert gas. Thanks tothis, the present embodiment can provide a positioning apparatus whichis lower in cost.

Next, description will be given below of a positioning apparatusaccording to a sixth embodiment of the present invention. FIG. 8 is afront section view of a positioning apparatus according to the sixthembodiment, with a differential pumping seal shown in a typified manner.FIG. 9 is a plan view of the present positioning apparatus and FIG. 10is a partially omitted enlarged section view of the periphery of thedifferential pumping seal having the structure shown in FIG. 8. Thepresent embodiment employs a structure in which a moving member can bemoved in a two-dimensional manner, that is, it can be moved in theX-axis direction and in the Y-axis direction extending at right anglesto the X-axis direction.

As shown in FIG. 9, the present positioning apparatus 410 comprises abox body 420 fixed by suitable means (not shown) and including anopening 420 a formed instead of the bottom wall thereof and a processchamber P formed in the interior thereof, a plate-shaped moving member430 disposed so as to shield the opening 420 a of the box body 420, adrive part 440 for moving the moving member 430 in a two-dimensionalmanner, a differential pumping seal 150, and a cover member 460. Theinterior of the process chamber P is sucked by a pump P1 through a pipe(shown in a simplified manner) to thereby provide a negative pressureenvironment.

The moving member 430 is supported by a bearing (not shown), can bemoved in the vertical direction and in the horizontal direction in FIG.10 by the drive part (for example, a combination of a motor and a ballscrew, or a linear motor) 440, and carries on the central portionthereof a table 431 for supporting a work (not shown). On the surface ofthe periphery of the opening 420 a of the box body 420 that is opposedto the moving member 430, there is disposed the differential pumpingseal 150 with a slight clearance between the moving member 430 anditself. More specifically, in FIG. 10, in the peripheral surface 420 dof the opening 420 a, there are formed a pair of grooves (differentialpressure chambers) 420 b, 420 b so as to extend along the entireperiphery of the peripheral surface 420 d. The interiors of the grooves420 b, 420 b can be respectively sucked by their associated exhaustpumps P2 (FIG. 8) through exhaust holes 420 c, 420 c penetrating throughthe side wall of the box body 420, so that the interiors of the grooves420 b, 12 b can provide negative pressure environment, respectively. Thenegative pressure environments can suck gas existing in the slightclearance between the peripheral surface 420 d of the opening 420 a andmoving member 430 to thereby be able to perform the sealing function.

As shown in FIGS. 9 and 10, the cover member 460 having an L-shapedsection is disposed over the entire periphery of the box body 420 insuch a manner that it covers the opening 420 a of the box body 420. To aspace formed in the interior of the cover member 460, there can besupplied the dry air from an air drier AD through a pipe 463. Thedimension of the cover member 460 is set such that, even when the movingmember 430 moves by the maximum amount, at least the portion of themoving member 430 moving into the interior of the process chamber P canbe prevented from moving externally of the cover member 460.

In the present embodiment as well, the exterior side of the opening 420a is covered with the cover member 460 and the interior of the covermember 460 is filled with the dry air (the air with the moisture removedtherefrom) supplied by the air drier AD to thereby turn the interior ofthe cover member 460 into the dry air environment, which makes itpossible to restrict the adsorption of the gas molecules (especially,the molecules of water) to the surface of the moving shaft 430 and thusmaintain the environment of the interior of the box body 420.

Next, description will be given below of a positioning apparatusaccording to a seventh embodiment of the present invention. FIG. 11 is apartially omitted section view of the periphery of a differentialpumping seal employed in a positioning apparatus according to theseventh embodiment. By the way, the seventh embodiment is different fromthe fifth embodiment mainly in that, instead of the cover member, thereis disposed a hydrostatic bearing having the function of the covermember. Therefore, description will be given mainly of the hydrostaticbearing and thus the duplicate description of the remaining portions isomitted here.

In FIG. 11, on the exterior side of the box body 320, adjacently to theopening 320 a, there is disposed a hydrostatic bearing 560. Thehydrostatic bearing 560 comprises a cylindrical-shaped support portion561 mounted on the box body 320 and a pair of ring-shaped jet-outportions 562, 562 made of porous material and disposed on the innerperiphery of the support portion 561. The jet-out portions 562, 562 areopposed to the surface of the moving shaft 330 with a slight clearancebetween them and jet out the dry air supplied from the air drier ADthrough a pipe 563 into the slight clearance. The support portion 561includes exhaust holes 561 a, 561 a which are disposed adjacent to thejet-out portions 562 and allow the inner and outer peripheries of thesupport portion 561 to communicate with each other. By the way,provision of the hydrostatic bearing 560 eliminates the need forprovision of the guide mechanism (not shown) for the moving shaft 330 inthe first embodiment. The dimension of the hydrostatic bearing 560 maybe preferably set such that, even in case where the moving shaft 330moves up to the maximum amount thereof, at least the portion of themoving shaft 330 moving into the interior of the process chamber P canbe prevented from moving externally of the hydrostatic bearing 560 (morepreferably, outwardly of the exterior side end portion position of thejet-out portion 562 situated near to the exterior side (the atmosphericenvironment side)).

In the present embodiment, when in operation, since the air suppliedfrom the air drier AD is jetted out from the jet-out portions 562 intothe slight clearance defined by and between the jet-out portions 562 andthe surface of the moving shaft 330, the moving shaft 330 is supportedin a floating state due to the pressure of the jetted-out air, wherebythe moving shaft 330 is supported in such a manner that it can be movedwith low friction. Also, because the space enclosed by the hydrostaticbearing 560 is filled with the dry air (the air with the moistureremoved thereof) supplied from the air drier AD, the adsorption of thegas molecules to the surface of the moving shaft 330 can be restrictedto thereby be able to maintain the environment of the interior of thebox body 320. According to the present embodiment, the support and guideof the moving shaft 330 as well as the formation of the dry airenvironment can be attained only by the hydrostatic bearing 560, whichcan contribute to a reduction in the number of parts.

(Description of the Results of Tests)

Now, description will be given below of the results of tests conductedby the inventors. FIG. 12 is a front section view of a positioningapparatus which is a test apparatus used in a test conducted by theinventors, while a differential pumping seal is shown in a typifiedmanner. The present positioning apparatus is similar to the positioningapparatus according to the sixth embodiment. However, since thestructure of the present positioning apparatus is simplified, the movingdirection of a moving member is set only in the right and left directionin FIG. 12.

As shown in FIG. 12, the present positioning apparatus 610 comprises abox body 620 including an opening 620 a formed instead of the top wallthereof and a process chamber P formed in the interior thereof, aplate-shaped moving member 630 disposed so as to shield the opening 620a of the box body 620, a drive part 640 for moving the moving member 630in the right and left direction in FIG. 12, a differential pumping seal650, and a cover member 660. The process chamber P is sucked by anexhaust pump P1 through a pipe shown in a simplified manner to therebyprovide a negative pressure environment.

The moving member 630 is supported by a bearing (not shown), can bemoved in the right and left direction in FIG. 12 by the drive part (forexample, a combination of a motor and a ball screw, or a linear motor)640. On the surface of the periphery of the opening 620 a of the boxbody 620 that is opposed to the moving member 630, there is disposed thedifferential pumping seal 650 with a slight clearance between the movingmember 630 and itself. More specifically, in FIG. 12, in the peripheralsurface 620 d of the opening 620 a, there are formed a pair of grooves(differential pressure chambers) 620 b, 620 b so as to extend along theentire periphery of the peripheral surface 620 d. The interiors of thegrooves 620 b, 620 b can be respectively sucked by their associatedexhaust pumps P2 through pipes which are shown in a simplified manner inFIG. 12 and penetrate through the side wall of the box body 620, so thatthe interiors of the grooves 620 b, 620 b can provide negative pressureenvironments respectively. The negative pressure environments can suckgas existing in the slight clearance between the peripheral surface 620d of the opening 620 a and moving member 630 to thereby be able toperform the sealing function.

As shown in FIG. 12, the box-shaped cover member 660 envelops the movingmember 630, while the cover member 660 covers the opening 620 a of thebox body 620 with such a sufficient dimension that does not interferewith the movement of the moving member 630. A connecting rod 641, whichallows the drive part 640 and moving member 630 to communicate with eachother, penetrates through a hole 660 a formed in the cover member 660.Also, to a space defined in the interior of the cover member 660, therecan be supplied a given kind of gas through a pipe 663 from an air drierAD (however, in the case of a comparison example 1 to be discussedlater, the air drier AD is removed and the air as it is introduced intothe process chamber P; and, in the case of a comparison example 2 to bealso discussed later, the air drier AD is replaced by a gas source whichis used to introduce nitrogen gas into the interior of the processchamber P).

Test conditions in the present test are as follows:

(1) Operation Pattern

-   -   0-70 sec: Moving member 630 stops.    -   70-150 sec: Moving member 630 reciprocates at a low speed (50        mm/sec)    -   150 sec-430 sec: Moving member 630 stops.    -   430 sec-600 sec: Moving member 630 reciprocates at a high speed        (100 mm/sec)    -   600 sec-: Moving member 630 stops.

(2) Test Environment

-   -   Room temperature (Box body outside temperature): 23° C.    -   Humidity (Box body outside humidity): 50%

Now, FIG. 13 is a graphical representation of the results of a testconducted on the comparison example 1 (in a state where nothing isconnected to the pipe 663) in which the air is supplied into the covermember 660. As shown in FIG. 13, the maximum value of variations in thepressure in the interior of the box body 620 was 2.1E-5 (whichcorresponds to 2.1×10⁻⁵; and, also which applies similarly hereinbelowas well) Pa.

Now, FIG. 14 is a graphical representation of the results of a testconducted on an embodiment according to the present invention in whichthe dry air is supplied from the air drier AD so that the dew-pointtemperature with respect to the atmospheric pressure can be −15° C. inthe exit portion from the air drier AD (in the interior of the covermember 660, the humidity of about 10%). As shown in FIG. 15, the maximumvalue of variations in the pressure in the interior of the box body 620was 0.54E-5 Pa.

FIG. 15 is a graphical representation of the results of a test conductedon the comparison example 2 in which there is used an inert gas(nitrogen gas) cylinder as a gas source, and nitrogen gas having adew-point temperature of −65° C. with respect to the atmosphericpressure (humidity of about 0.04% in the interior of the cover member660) was supplied to the interior of the cover member 660. As shown inFIG. 11, the maximum value of variations in the pressure in the interiorof the box body 620 was 0.33E-5 Pa.

From the above test results, it has been found that, in the case of thepresent embodiment, when compared with the case in which the interior ofthe cover member 660 is filled with the air (atmospheric pressure),since the interior of the cover member 660 is filled with the dry air,variations in the pressure can be reduced up to 30%. Also, when the casein which the interior of the cover member 660 is filled with the dry airis compared with the case in which the interior of the cover member 660is filled with the inert gas, the latter case using the inert gas isbetter in restricting the variations in the pressure than the formercase using the dry air; however, the difference between them is small.On the other hand, in case where the gas to be supplied is the air,there is no need for provision of a facility for collecting the airafter it is exhausted. That is, when taking the cost of the facilitiesinto consideration, it has been found that the structure according tothe present embodiment is advantageous over the structure using theinert gas.

By the way, as described above, the dry air with humidity of 10% canprovide sufficient performance (that is, can maintain the environment ofthe interior of the process chamber). However, in case where thehumidity is reduced down to a level of less than 10%, of course, therecan be obtained better results. For example, as an air drier, there isavailable an air drier of a heatless type which can obtain the airhaving a dew-point temperature of −50° C. In case where the air drier ofa heatless type is used, the humidity can be reduced down to about 0.5%.

Although description has been given hereinbefore of the preferredembodiments of the present invention, the present invention is notlimited to these embodiments but, of course, various changes andimprovements are also possible. For example, in the above embodiments,the term “moving member” means a member which moves with respect to thebox body. However, instead of the moving member, the box body may bedriven or moved.

Description will be given below of an eighth embodiment of a positioningapparatus according to the present invention with reference to theaccompanying drawings. FIG. 16 is a front section view of a positioningapparatus according to the eighth embodiment of the present invention,while a differential pumping seal is shown in a simplified manner. Bythe way, the eighth embodiment is different from the first embodimentmainly in that, the entire portions of the moving block 30 or theportions of the moving block 30 that correspond to areas S1 are formedof close-density material. Therefore, the duplicate description of theremaining portions is omitted here.

Now, as described above, FIG. 2 is an enlarged section view of theperiphery of the first differential pumping seal 50, showing theabsorption or occlusion and elimination of gas molecules in a typifiedmanner. The first differential pumping seal 50 includes openings 51, 52opposed to the surface of the moving block 30 and passages 53, 54 incommunication from the openings 51, 52 to a pump P2 which is disposedexternally of the positioning apparatus. Here, in case where the wholemoving block 30 is formed of porous ceramic material, there is a fearthat the following problems can arise.

In case where the moving block 30 moves to the left in FIG. 2, since theupper surface of the moving block 30 is formed of porous material, amajor part of the absorbed or occluded gas molecules Am are sucked whenthey become opposed to the opening 52 due to the movement of the movingblock 30; and further, when they become opposed to the opening 51,almost all of the remaining occluded gas molecules Am are sucked.However, the unsucked remaining occluded gas molecules Am can beeliminated in the interior of the process chamber P, thereby raising afear that the negative pressure (or specific gas) environment of theprocess chamber P can be impaired. Therefore, in case where the entireportions of the moving block 30 or the portions of the moving block 30that correspond to areas S1 are formed of close-density material, theabsolute quantity of gas molecules Am to be adsorbed or occluded to thesurface of these portions can be reduced as much as possible, therebybeing able to solve the above problem.

Next, description will be given below of the ninth embodiment of apositioning apparatus according to the present invention. The presentembodiment is similar in structure to the first embodiment but isdifferent therefrom in that the mother material of a moving block 30serving as a moving member according to the present embodiment iscomposed of porous ceramic material and the required portions of themoving block 30 are covered with coatings. In this case, not only themoving block 30 is light in weight and high in rigidity, but also therecan be obtained the following advantages. That is, in FIG. 16, the areasS1 of the upper surface of the moving block 30, which are disposed withthe first differential pumping seals between them, are able to move intoor out of the process chamber P as the moving block 30 moves and,therefore, the areas S1 are exposed not only to be atmospheric pressureenvironment but also to a negative pressure environment (or a specificgas environment). Accordingly, in the present embodiment, the surfacesof the areas S1, which are formed of normal ceramic material and thus inwhich adsorption and elimination of the gas molecules Am are easy tooccur, are coated with CVD films, thereby being able to control theadsorption of the gaseous molecules Am. This provides an outstandingeffect that the environment of the interior of the process chamber P canbe protected effectively. Such coating is especially effective on thehigh-vacuum side which is equal to or higher in vacuum than 10⁻³ Pa. Bythe way, of course, the entire upper surfaces of the moving block 3, orthe entire upper surfaces of the moving block 30, or the entire interiorportion of the moving block 30 including the areas S1 of the uppersurfaces thereof can also be coated with the CVD films. Referring to theportions which exist inside the areas S1, in case where they are washedsufficiently before they are inserted into the interior of the processchamber P for the first time, since they are always present within theprocess chamber P from that time on, they raise no problem even when theporous mother material is exposed to the surfaces thereof; however, incase where these portions are also coated with the CVD films, there isobtained an advantage that the above-mentioned pre-treatment can beexecuted in a short time. The thickness of the coating may be thethickness that not only can prevent the permeation of the gas (gasmolecules) through the coating but also can provide proper surfaceroughness.

Further, description will be given below of a device for restricting thedeformation of the moving block 30. Firstly, let us assume a case inwhich the second box body 40 is omitted. In this case, since theatmospheric pressure (about 10⁵ Pa) is always acting on the lowersurface of the moving block 30, the central portion of the upper surfaceof the moving block 30 is deformed in such a manner that it is pulledupwardly in FIG. 1. Even in case where such deformation is slight,because the height position of the table 31 varies, it is difficult towork a work with high accuracy.

On the other hand, in the above-mentioned first and second embodiments,since the second box body 40 is disposed opposed to the first box body20 and the decompression chamber R formed in the interior of the secondbox body 40 is held in the negative pressure environment, the lowersurface of the moving block 30 is pulled downwardly in FIG. 1 to therebyrestrict the deformation of the moving block 30 due to the negativepressure of the process chamber P, which makes it possible to keep themoving block 30 substantially in a no-deformation state. Therefore,since the height position of the table 31 is prevented from varying, thework positioning with high accuracy can be attained. Also, because theopenings 20 a and 40 a are formed to have the same shape and aredisposed opposed to each other, the deformation mode of the moving block30 can be made to balance well and thus further-higher-accuracypositioning can be accomplished.

By the way, the degree of vacuum of the decompression chamber R need notbe coincident with the degree of vacuum of the process chamber P; forexample, when the pressure of process chamber P is set at 10⁻⁵ Pa, evenin case where the pressure of the decompression chamber R is set about10⁻⁴ Pa (about 1/10 of the atmospheric pressure), the degree ofdeformation of the moving block 30 can be reduced down to about 1/10 ofthe degree of deformation that occurs in the structure excluding thedecompression chamber R. Thanks to this, as the pump P3 of thedecompression chamber R, there can be used a pump which is lower incapacity and lower in cost, which makes it possible to reduce the costof the positioning apparatus. However, in case where there is formed inthe moving block 30 a passage which allows the decompression chamber Rand process chamber P to communicate with each other, there can beomitted the pump P3 for the decompression chamber R. In this case, notonly the areas S1 but also the areas S2 must be coated with the CVDfilms. By the way, in the second embodiment, in case where as the mothermaterial, instead of ceramic material, there is used metal material suchas stainless steel or aluminum alloy, there can be obtained an effectthat the gas molecules Am can be restricted from moving into the processchamber P. In this respect, the moving block 30 may also be formed ofmetal material.

Although description has been given heretofore of the present inventionusing the preferred embodiments thereof, the present invention is notlimited to these embodiments but, of course, various changes andimprovements are also possible. For example, the moving block 30 mayalso be structured such that it is able to move not only in the rightand left direction in FIG. 1 but also in a direction perpendicular tothe figure sheet (that is, it is able to move in a two-dimensionalmanner). Or, the moving block 30 can be made of a round shaft so that itcan be moved in the axial direction thereof to move into and out of anopening formed in a box body. However, it makes little sense to applythe present invention to a structure in which the round shaft cannot bemoved in the axial direction thereof but it can be only rotated.

In addition, in the first to seventh embodiments, the surface of theportion of the moving member, which is the moving block 30, 430, theround shaft 130,230,330 and so on, to be moved into at least theinterior of the process chamber may be formed of high-density materialor coated with the CVD firm or the PVD film as shown in the eighthembodiment. According to the above composition of the moving member,since either absorption or occlusion of the gas molecules or the likedoes not happened quite often, it can certainly prevent the gasmolecules or the like from intruding into the process chamber P.

For example, in the third embodiment, with respect to the maximum strokeamount S of the round shaft 130, when the distance from the inner wall120 b of the process chamber P to the inner wall 151 a of the peripheralgroove 151 (or to the inner wall 152 a of the peripheral groove 152) isexpressed as a distance c (or d), the distance c (or d) is set in such amanner that the relationship S≦c (or S≦d) can hold. According to theabove composition, the positioning apparatus can be applied to theprocess chamber with strict condition. However, in the case of thesurface of the round shaft 130 to be moved into at least the interior ofthe process chamber is formed of high-density material or coated withthe CVD firm or the PVD film, under the terms, if S≦b is hold as shownin the second embodiment, the positioning apparatus can be applied tothe process chamber with strict condition shown in the same of the thirdembodiment.

As has been described heretofore, a positioning apparatus according tothe present invention comprises a box body including not only a processchamber formed in the interior thereof but also an opening allowing theprocess chamber to communicate with the outside, a moving memberdisposed so as to shield at least part of the opening and movable withrespect to the opening of the box body, and a differential pumping sealfor sealing a clearance between the box body and moving member, inwhich, when the moving member moves, in order to prevent the portion ofthe moving member that is exposed to the outside of the box body frombeing moved into the interior of the process chamber, the width of theportion of the box body that is opposed to the moving member in themoving direction of the moving member is set equal to or larger than themoving amount of the moving member. Thanks to this, even in case wheregas molecules are adsorbed to the surface of the moving member exposedto the exterior of the process chamber, since the present surface isprevented from moving into the interior of the process chamber, theenvironment of the interior of the process chamber can be protected.

In addition, since the above effect can be accomplished without using aparticular material for the moving member, the present invention has anadvantage of the production cost.

The researches made by the inventors have shown that, in case where thedry air (the air with the moisture component removed therefrom) is usedas the environment to which the portion of the moving member movableinto and out of the interior of the process chamber is exposed, theamount of gas to be released into the interior of the process chambercan be restricted as effectively as when the inert gas is used toprovide such environment. Since the dry air can be obtained by removingthe moisture from the air, when compared with creation of the inert gasenvironment, formation of the dry air environment can reduce the timeand labor for management and cost thereof greatly.

As has been described heretofore, a positioning apparatus according tothe first aspect of the present invention comprises a box body includingnot only a process chamber formed in the interior thereof so as to beexposed to a decompressed environment but also an opening for allowingthe process chamber to communicate with the outside, a moving memberformed of ceramic material such that it can shield at least part of theopening of the box body and it is able to move with respect to theopening of the box body, and a differential pumping seal for sealing theopening of the box body and moving member with respect to each other,while close-density material is disposed on the surface of the portionof the moving member that is allowed move between the interior andexterior of the process chamber. Since as the mother material of themoving member, there is used ceramic material which is light in weight(low in specific gravity) and is high in rigidity, the deformationamount of the moving member can be restricted and thus the positioningaccuracy of the positioning apparatus can be enhanced. Also, because theceramic material is non-magnetic material, especially when an ion chargeapparatus or an electronic beam apparatus requiring a vacuum environmentand low magnetic field variations is used in working a work in theinterior of the process chamber, there can be provided a more suitablepositioning apparatus. In addition to this, since the close-densitymaterial is disposed on the surface of at least the portion of themoving member movable between the interior and exterior of the processchamber, the adsorption of the gas molecules can be restricted tothereby be able to protect the environment of the interior of theprocess chamber.

Also, a positioning apparatus according to the second (or third) aspectof the present invention comprises a box body having not only a processchamber formed in the interior thereof so as to be exposed to adecompressed environment but also an opening for allowing the processchamber to communicate with the outside, a moving member formed ofceramic material (or metal material) such that it can shield at leastpart of the opening of the box body and it is able to move with respectto the opening of the box body, and a differential pumping seal forsealing the opening of the box body and moving member with respect toeach other, while a close-density coating is disposed on the surface ofthe portion of the moving member that is allowed to move between theinterior and exterior of the process chamber. Therefore, in case where,as the mother material of the moving member, there is used ceramicmaterial which is light in weight (low in specific gravity) and is highin rigidity, the deformation amount of the moving member can berestricted and thus the positioning accuracy of the positioningapparatus can be enhanced. Also, since the ceramic material isnon-magnetic material, especially when an ion charge apparatus or anelectronic beam apparatus requiring a vacuum environment and lowmagnetic field variations is used in working a work in the interior ofthe process chamber, according to the present aspect of the presentinvention, there can be provided a positioning apparatus which isfurther suitable for this purpose. In addition to this, because theclose-density coating is disposed on the surface of the portion of themoving member that is allowed to move between the interior and exteriorof the process chamber, the adsorption and elimination of the gasmolecules can be restricted to thereby be able to protect theenvironment of the interior of the process chamber.

1. A positioning apparatus, comprising: a box body including a processchamber exposed to a decompression environment in the interior of thebox body and an opening allowing said process chamber to communicatewith an area outside of the box body; a moving member for shielding saidopening of said box body with a slight clearance between said box bodyand the moving member and movable with respect to said opening of saidbox body; a driving portion that moves said moving member; and adifferential pumping seal for sealing said slight clearance between saidopening of said box body and said moving member, wherein on a portion ofsaid moving member to be moved into the interior of said processchamber, when said moving member moves, there is formed a treatedsurface that restricts an amount of emission gas accumulatable thereon,and wherein a width of a portion of said box body opposed to said movingbody in a moving direction of said moving member is set equal to orlarger than a moving amount of said moving member.
 2. The positioningapparatus as set forth in claim 1, wherein a seal surface of saiddifferential pumping seal on said box body side includes a plurality ofgroove portions so formed as to surround said opening, and saidplurality of groove portions are respectively formed so as tocommunicate with their associated exhaust passages, and also wherein thewidth of the near-to-process-chamber end of one of said groove portionsbeing most distant from said process chamber to said process chamber inthe moving direction of said moving member is set equal to or largerthan the moving amount of said moving member.
 3. The positioningapparatus as set forth in claim 2, wherein a hydrostatic bearing usinginert gas as a medium is disposed in combination with said differentialpumping seal so as to adjoin the side of said differential pumping sealsituated near to an outside.
 4. The positioning apparatus as set forthin claim 1, wherein a hydrostatic bearing using inert gas as a medium isdisposed in combination with said differential pumping seal so as toadjoin the side of said differential pumping seal situated near to anoutside.
 5. A positioning apparatus, comprising: a box body including aprocess chamber exposed to a decompression environment in the interiorof the box body and an opening allowing said process chamber tocommunicate with an area outside of the box body; a moving member forshielding said opening of said box body with a slight clearance betweensaid box body and the moving member and movable with respect to saidopening of said box body; a driving portion that moves said movingmember; and a differential pumping seal for sealing said slightclearance between said opening of said box body and said moving member,wherein on a portion of said moving member to be moved into the interiorof said process chamber, when said moving member moves, there is formedas an adsorption preventive area, and wherein a thickness of a portionof said box body opposed to said moving body, in a moving direction ofsaid moving member, is set equal to or larger than a maximum movingamount of said moving member.
 6. The positioning apparatus as set forthin claim 5, wherein said adsorption preventive area is a treated surfacethat restricts an amount of emission gas accumulatable thereon.
 7. Thepositioning apparatus as set forth in claim 5, wherein a seal surface ofsaid differential pumping seal on said box body side includes aplurality of groove portions so formed as to surround said opening, andsaid plurality of groove portions are respectively formed so as tocommunicate with their associated exhaust passages, and also wherein thedistance, in the moving direction of said moving member, between: thenear-to-process-chamber end of the one of said groove portions beingmost distant from said process chamber; and said process chamber, is setequal to or larger than the maximum moving amount of said moving member.